In the production of a filled snack having soft, moist filling, such as a fruit filling, using a high moisture content filling, the moisture migrates between, the filling and the casing until the water activity or relative humidity of the filling and casing are the same at equilibrium. Generally, it may take from several days to several months for equilibrium to be reached when the snack is packaged in moisture proof packaging. A baked good may be made crisp by baking to a low moisture content. For example, a toaster pastry or a piece of bread may be made crisp by toasting to a low moisture content. When moisture migrates from a high moisture content filling to a low moisture content casing, the casing texture may lose crispness and become soft and moist. In some snack products, such as FIG NEWTONS®, a moist soft filling and a moist soft baked casing are desirable. However, to produce a filled baked snack having a crisp casing and a soft moist filling, use of a high moisture content filling generally softens a crisp casing to the point where it is no longer crisp. To remedy this problem, the amount of high moisture filling may be substantially reduced or the snack product may be cooked, baked or toasted, like a toaster pastry product, to reduce the moisture content of the casing and develop crispness. However, reduction of the amount of a high moisture content filling or reducing the moisture content of a filling to increase crispness of the casing, detracts from the attainment of a soft, moist, lubricious mouthfeel or texture for the filling. Also, cooking or toasting of the product requires an extra step by the consumer, and the convenience of a ready-to-eat product is lost. Further heating of the product, such as by toasting or microwaving to reduce the moisture content of the casing may also substantially reduce the moisture content of the filling resulting in loss of a moist, soft mouthfeel for the filling. The heating may also cause undesirable escape or leakage of the filling from the casing, especially in a product having open ends with a visually apparent filling, such as a FIG NEWTON®.
Reduction of moisture migration by the use of a moisture barrier material is disclosed in U.S. Pat. Nos. 4,715,803 and 4,748,031 to Koppa. An extruder provides a triple coextruded product having an inner layer, which is surrounded, or enrobed, by an intermediate layer, which is surrounded, or enrobed, by a third outer-most layer. The inner layer is a dough having a chewy and moist texture when baked and the outer layer is a dough having a crispy texture after baking. A barrier material is injected between the two dough layers to achieve the desired product stability and shelf life. However this approach requires special extrusion equipment and introduces a barrier material into the formulation.
It is believed that as moisture migrates in increasing amounts to a baked casing, the glass transition temperature (Tg) of casing ingredients, such as starch, is increasingly reduced. As the glass transition temperature (Tg) is reduced, such as to below body temperature (e.g. 37° C.) or below room temperature, the ingredient melts or changes phase to impart a softer texture or mouthfeel with a loss of crispiness.
Glass transition can be defined as a physicochemical event or change of state that can govern product properties. See “A History of the Glassy State in Foods”, ed. Blanshard & P. J. Lillford. Univ. Nottingham Press, Nottingham, UK, pp. 1-12 (1983). Glass-forming aqueous food polymers mediate the thermal, mechanical and structural properties of food. Plasticization by low molecular weight solvents like water modulates the temperature location of the glass transition of aqueous food polymers. See, Sears & Darby, The Technology of Plasticizers, Wiley-Interscience New York (1982); Slade & Levine, “Structural stability of intermediate moisture foods—a new understanding?;” Food Structure-Its Creation and Evaluation, eds. J. M. V. Blanshard and J. R. Mitchell, Butterworths, London, pp. 115-47, (1989); a food polymer science approach to selected aspects of starch gelatinization and retrogradation. In Frontiers in Carbohydrate Research-1: Food Applications, ed. R. P. Millane, J. N. BeMiller and R. Chandrasekaran, Elsevier Applied Science, London, pp. 215-70) it is disclosed that water depresses the Tg of completely amorphous or partially crystalline food products. As explained by Slade & Levine, structure-property relationships for food materials during processing and product storage are affected by thermal glass transition temperature
Thermal glass transition defines the temperature above which a viscoelastic, rubbery liquid state of accelerated mobility exists and below which a glassy, brittle low mobility state occurs. (Slade & Levine, A polymer science approach to structure/property relationships in aqueous food systems: non-equilibrium behavior of carbohydrate-water systems, Water Relationships in Foods, eds. H. Levine and L. Slade. Plenum Press, New York, pp. 29-101 (1991)
Also, Tg varies with molecular weight (MW) impacting mechanical properties. Tg increases with increasing number average MW (Mn), up to a plateau limit for the region of entanglement coupling in rubber-like viscoelastic networks typically at Mn=1.25×103 to 105 and then levels off. See, Graessley, Viscoelasticity and flow in polymer melts and concentrated solutions, Physical Properties of Polymers, eds. J. E. Mark, A. Eisenberg, W. W. Graessley, L. Mandelkem and J. L. Koenig. American Chemical Society, Washington D.C., pp 97-153 (1984). It should be noted that Tg values can vary substantially even within a series of compounds of the same molecular weight and similar structure.
It is well known that water, acting as a plasticizer, affects the Tg of completely amorphous polymers and both the Tg and Tm of partially crystalline polymers. See, Rowland, Water in Polymers, ACS Symp. Ser. 127, American Chemical Society, Washington, D.C. (1980). The direct plasticizing effect of increasing moisture content at constant temperature is equivalent to the effect of increasing temperature at constant moisture and leads to increased mobility allowing a primary structural relaxation transition at decreased Tg (Rowland, 1980)
Atkins, Basic principles of mechanical failure in biological systems, Food Structure and Behaviour, eds. J. M. V. Blanshard and P. Lillford. Academic Press, London, pp. 149-76 (1987) discloses that water plasticizer drops the Tg of most biological materials from about 200° C. (for anhydrous polymers starch, gluten, gelatin (Levine & Slade 1988) to about −10° C. at or above moisture contents near 30% (Levine & Slade 1988). For high biopolymers dry Tg is about equal to 200° C.; and the Tg decreases by 10° C.+/−5° C. for every wt % water at low moisture contents; and Tg is about room temperature at about 20% moisture.
There is a published thermal glass transition curve of gelatinized waxy corn starch as a function of moisture content from about 10% to about 25% in Kalichevsky, The glass transition of amylopectin measured by DSC, DMTA and NMR Carbohydr. Polym, 18, 77-88 (1992.). Le Meste,. Glass transition of bread. Cereal Foods World, 37, 264-7 (1992) published glass transition of white pan bread reported in terms of onset temperature for softening by TMA. Tg vs. moisture content for bread which begins at 165° C. and decreases by 10° C./wt % moisture from 0 to 10%; and by 5° C./wt % water from 10 to 20% moisture thereby passing through Tg=20° C. at 16.6% water.
As disclosed in U.S. Pat. No. 4,455,333 to Hong et al, the type and amount of sugar may be used to manipulate sugar crystallization to control texture of a baked good. For example, sucrose is a crystallizable sugar and provides a crisp texture to baked goods, whereas humectant sugars such as high fructose corn syrup provide a soft or chewy texture to baked goods. U.S. Pat. No. 5,080,919 to Finley et al discloses that maltodextrins impart brittleness, but in combination with humectants provides a crisp texture and good cookie spread.
Sugar behaves as a plasticizing co-solvent with water, but less so than water alone so that the gelatinization temperature in the presence of sugar is higher relative to the gelatinization temperature of starch in water alone. The antiplasticizing effects of sucrose and other sugars on the gelatinization of native starches are published (Slade Levine 1987).
A published state diagram for sucrose-water (Slade & Levine, Beyond water activity: recent advances based on an alternative approach to the assessment of food quality and safety. Crit. Rev. Food Sci. Nutri., 30, 115-360 (1991) is relevant to manufacturing of cookies and crackers, where finished product texture is dependant in part on the structure function relationships of sucrose as well as flour polymers.
Amemiya, J. & Menjivar, J. A., Mechanical properties of cereal-based food cellular systems. American Association of Cereal Chemist, 77th Annual Meeting, abs. 207, September. 22, Minneapolis, Minn.; ((1992), and Slade & Levine, Journal of Food Engineering 24 pp. 431-509; page 477, (1995) disclose a room temperature glass transition occurring at a moisture content at 10% in a cracker formula with virtually no low MW sugars for which the continuous amorphous matrix would be a three dimensional network of developed gluten and gelatinized starch (the latter comprising 70% of the total starch content of the flour) to about 8% moisture Tg room temperature for a rich cracker formulated with sugar.
U.S. Pat. No. 5,523,106 to Gimmler et al discloses raising the glass transition temperature (Tg) of a fruit juice snack having a cookie-like texture. A starch hydrolyzate (e.g. maltodextrin) and a pregelatinized starch are used to adjust Tg and provide a crispy texture. The glass transition temperature (Tg) for the final product is above room temperature, preferably at least about 30° C. and less than or equal to about 60° C.
U.S. Patent Application No. US20020039612 A1 to Gambino et al discloses a baked toastable freezer stable filled waffle. The filled waffle has a batter-based outer casing material that surrounds an inner filling material. Utilization of a filling material having a water content and water activity level below that of the outer casing material enables the formation of a toastable freezer stable filled waffle. The filled waffle can be stored frozen and reheated rapidly in a conventional toaster without burning or charring of the outer casing material and complete heating of the inner filling material.
International Patent Publication No. WO 0511266A1 to Roberts et al discloses a microwaveable food product that is adapted to be cooked or heated prior to consumption. The food product includes a core of filling which generates moisture on cooking or heating, an outer coating adapted to crisp on cooking or heating, and at least one intermediate barrier layer arranged between the core and the coating. The intermediate barrier layer is adapted to substantially prevent migration of moisture between the core and outer coating upon cooking or heating of the product. The intermediate barrier layer includes at least one layer of pasta.
U.S. Patent Application Publication No. US2005/0084567 A1 to Brown et al discloses a dough and a filling for making a toaster pastry. The dough for the toaster pastry is made by forming a blend of ingredients comprising wheat flour of from about 25 to about 44% by weight of ingredients for the dough, wheat farina of from about 13 to about 35% by weight of ingredients for the dough, shortening of from about 1.5 to about 2.5% by weight of ingredients for the dough, and water of from about 25 to about 35% by weight of ingredients for the dough; adding puff pastry shortening in the form of cubes such that the amount of puff pastry shortening is in the range of from about 5 to about 15% by weight of the ingredients for the pastry; and blending the ingredients such that a heterogeneous mixture of the cubes of shortening in the remainder of the ingredients is obtained. The dough is formed into a layered structure, the layered structure comprising a single base sheet of the dough covered with a pastry filling, with a single top sheet of the pastry blend of the dough applied thereover.
U.S. Pat. No. 6,267,998 to Baumann et al discloses a fully baked or fried multi-layered toaster product having a first layer and a second layer wherein the first and second layers are constructed of dissimilar materials. The first layer provides the structural properties required for a toaster product while the second layer provides enhanced characteristics such as taste, texture, and other organoleptic properties. The multi-layered toaster product contains dissimilar dough or batter types and can further include filling and/or particulates and/or toppings.
U.S. Patent Application Publication No. US2005/0249845 A1 to Mihalos et al disclosed a process for preparing filled cracker snacks containing a creamy, lubricious low water activity, and bake stable filler encased within a crisp oven-baked cracker with efficiency and consistency despite the difficult rheology of the filler. A smooth textured, bakable filling is prepared comprising an oil phase, an aqueous phase and a solids phase by blending the ingredients and mixing with high shear to form a homogeneous filler having a viscosity of greater than 1.5×105 centipoise. Also prepared are top and bottom sheets of cracker dough, the bottom of which is moved at a predetermined horizontal velocity for depositing a plurality of continuous or intermittent streams of a bakable filling thereon from a depositor comprising a plurality of openings. The top dough sheet is then placed over the bottom sheet, and the sheets are cut and/or scored in a predetermined pattern to form a composite unbaked dough and filling. Finally, the composite is baked sufficiently to provide a crisp outer crust that exhibits textural and microbiological stability.
The present invention provides a shelf-stable filled, baked crispy snack, such as a fruit filled cracker, which has a baked casing which is crisp over extended periods of time even though both the baked casing and the baked filling have a high moisture content, and the filling is present in large amounts. The textural dichotomy of a crispy baked casing and a moist, soft filling is achieved over extended periods of time without the need for a moisture barrier between the casing and the filler. Use of a triple coextrusion device for providing a moisture barrier is not required. The product may be produced using conventional dough sheeting and filling depositing equipment. The baked snack of the present invention is ready-to-eat out of the packaging and does not have to be toasted, microwaved or further baked, cooked, or heated for consumption, or to achieve a crisp textured casing. The casing remains crisp at temperatures substantially above room temperature and human body temperature. The filled, baked crisp snack may be produced with open ends to provide a visually apparent filling, and filling may be deposited so that it extends to the edges of the casing all without causing leakage or running of the filler from the casing.